Sudden Infant Death Syndrome: New Clue

July 3, 2008 -- A new clue to the cause of sudden infant death syndrome (SIDS) comes from baby mice that suddenly die when their brain serotonin levels go haywire.

Serotonin is a signaling chemical that has far-reaching effects in the brain and other organs. But while too much or too little serotonin can cause many kinds of problems, death wasn't supposed to be one of them. Until now.

Cornelius Gross, PhD, and colleagues at the European Molecular Biology Laboratory near Rome genetically engineered mice to have abnormally low levels of serotonin. They didn't think this would kill the mice. After all, genetically engineered mice with no serotonin at all manage to survive.

But Gross' team was amazed to see that many of their mice did indeed die -- at an early age roughly equivalent to the age range at which human infants succumb to SIDS -- 1 month to 1 year old.

"The similarity to SIDS is there is sudden death during a restricted period of early life -- and it is caused by a change in the serotonin system," Gross tells WebMD.

During early life, Gross' mice appeared to be normal. Then they underwent a series of "crises" during which their heart rate and body temperature unpredictably dropped. More than half of their mice died during one of these crises.

What triggered the crises? Gross doesn't know, but he suspects that the crises were most likely to occur during the transition from sleep to wakefulness.

Gross is quick to point out that what's wrong with his genetically engineered mice isn't the same thing that happens when kids die of SIDS. The mice carry an overactive gene that signals the body to make less serotonin. SIDS kids have no such overactive gene.

Even so, the finding suggests that researchers who have previously linked serotonin to SIDS are on the right track.

"Maybe there is some kind of signature we could find in these mice before they have a crisis, some way they respond when they wake up from sleep," Gross says. "That might help us identify those kids most at risk of SIDS and provide parents with some kind of monitoring to catch them before a crisis occurs."

Gross and colleagues report their findings in the July 4 issue of the journal Science.